Oxidation of isobutylene to methacrylaldehyde over complex vanadium oxide catalysts



United States Patent OXIDATION OF ISOBUTYLENE T0 METHACRYL- ALDEHYDEOVER COMPLEX VANADIUM OXIDE CATALYSTS Donald M. Coyne, Prairie Village,and Roger P. Cahoy,

Merriam, Kans., assignors to Gulf Research & Development Company,Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.Continuation-impart of application Ser. No. 247,307, Dec. 26, 1962. Thisapplication Apr. 12, 1966, Ser. No. 542,118

Int. Cl. C07c 45/04; B013 11/84, 11/32 U.S. Cl. 260604 This applicationis a continuation-in-part of US. Patent applications Ser. No. 208,637,filed July 9, 1962, and now abandoned, and Ser. No. 247,267, Ser. No.247,268, and Ser. No. 247,307, filed Dec. 26, 1962, all now abandoned.

The present invention is directed to the oxidation of 2 methylpropene(isobutylene) to methacrylaldehyde (methacrolein) with maximumselectivity and catalyst life, with minimum expense for catalystreplacement and without the necessity of using purified isobutylene asraw material.

In U.S. Ser. No. 208,637 the applicants disclosed the oxidation ofisobutylene by contacting a gaseous feed stream consisting ofisobutylene, air and steam with a novel metal oxide catalyst complex,for example, a composition having the empirical formula Cu Te PV 0supported on lumps of cemented silicon carbide aggregate. The use of acatalyst composition having the empirical formula Cu Te V O is alsospecifically exemplified in the application to demonstrate theeffectiveness of simple compositions based only on the metal oxideswhich are essential for production of the catalyst for isobutyleneoxidation. In the prior application the conversion of isobutylene atrates in excess of 40 percent with a corresponding yield (selectivity)in excess of 50 percent are exemplified, specifically, to illustrate thetype of results which are obtained by the disclosed process.

Briefly, our process for converting isobutylene to methacrolein may bedescribed as comprising reacting isobutylene at a temperature within therange of about 350 to 525 C. in the presence of oxygen and a metal oxidecomposition produced by heating an intimate mixture consistingessentially of oxides of copper, vanadium and tellurium to a temperatureat least as high as that employed in converting isobutylene tomethacrolein, said oxides 'be ing present in a ratio of about 1 to 20moles of copper oxide to vanadium oxide, said metal oxide compositionsbeing on the surface of a refractory solid which is essentiallynon-reactive with respect to the metal oxide composition and possesses asurface area of less than about square meters per gram.

So that the process may be better understood, there is presented below adetailed discussion with illustrative examples.

1 Claim (A) THE CATALYST Before operating the process, it is necessaryto obtain a quantity of the catalyst, which is of an unusual type,possessing some unique characteristics. The selection of the particularmetal oxide composition for the purpose is based on its ability toconvert isobutylene to methacrolein With high selectivities, even whenhigh conversion rates are maintained, so that continuous operation withrecovery and recycling of unreacted isobutylene can be accomplished witha minimum production of tars and byproducts. The preferred metal oxidecompositions are capable of extraordinarily high yields of methacroleinper pound of active catalyst. Consequently, small differences in theprice of the catalyst raw materials have no great economic significance,unless they directly affect the uselCC ful life or the overall activityof the catalyst. The selection of raw materials for catalyst manufactureis therefore based mainly on these factors, as well as convenience.

(1) Catalyst carrier or support.Tl'ie catalyst support is selected fordurability and enhancement of catalyst activity and life. Siliconcarbide aggregate consisting of crystals of silicon carbide cementedtogether to form porous masses has been found to possess the bestcombination of properties. However, other refractory solids which arenon-reactive with respect to the metal oxide composition such as, forexample, alumina and zirconium silicate can be employed, providing theyhave a surface area of less than about 10 square meters per gram andpreferably less than 5 square meters per gram. The size and shape ofparticles of catalyst support are selected so as to minimize packing,clogging and formation of large cavities in the catalyst bed.

(2) Catalyst composition.The catalyst composition which is coated on thesupport is of the metal oxide type, consisting of a complex systemresulting from interaction of oxides of copper, vanadium and tellurium.A suitable composition can be prepared, for example, by forming anintimate mixture of these oxides in the proportions indicated below,followed by interaction at elevated temperature:

Moles CuO 1-20 TeO 0.0110 V0 12 The empirical formula of the catalystmay vary over rather broad limits, as indicated by the above ranges ofproportions. Although the composition of the cata lytically active sitesin such a composition may have a specific empirical formula, this wouldbe difiicult to prove. -A preferred catalyst has limits of compositionas indicated 'below:

9 1 1'5 o-z i-i o-i iz appmms The oxygen content of the compositionexhibits some variability and is difficult to determine accurately.Since metal oxides in general are non-stoichiometric compositions, somevariability in the oxygen analysis is not unusual. An intimate mixtureof metal oxides may conceivably be made by grinding or mulling followedby heating. However, the preferred method of manufacture is to preparean aqueous solution of water-soluble compounds of copper, tellurium andvanadium, coat the solution on a carrier, evaporate the water and thenbeat the dried solid material. In the preferred method of catalystmanufacture, differential thermal analysis indicates that at least onereaction occurs at temperatures substantially lower than thetemperatures at which the isobutylene oxidation process is customarilyoperated. For instance, in manufacturing the composition set forth aboveby empirical formula, the dried coating of soluble salts appears toundergo reactions within the range of about to C. to yield a product ofapparently stable composition. For want of a better descriptive termthis product is called an intimate mixture of metal oxides. Although thebest performing products have rather definite empirical formulas and areobtained by means of chemical reactions, they are very diflicult tocharacterize. The profuseness of peaks obtained by X-ray diffractionappears to indicate an extremely complex molecular or crystallinestructure (a very large number of ordered spatial arrangements ofatoms). Occasionally a sample of this intimate mixture of metal oxidesgives indication of undergoing another reaction at about 350 C., whichis apparently irreversible during the normal useful life of thesubstance as a catalyst.

For the sake of convenience in producing an adherent coating of uniformcomposition on the catalyst support, it is preferred to employwater-soluble metal salts in homogeneous solution. Preferably, these aresalts such as nitrates, phosphovanadates, vanadates, tellurates andammonia complexes, which decompose very readily to form an intimatemixture of metal oxides. If true homogeneous solutions are not readilyobtainable with materials at hand, undissolved components may beincorporated as dispersed or suspended particles with satisfactoryresults.

Following is a suitable procedure for preparation of the preferred typeof catalyst.

Example I A hot solution is made containing 16 g. of ammoniumphosphovanadate [prepared by the process described by A. Rosenheim andM. Pieck, Z. Anorg. Allgem. Chem. 98, 223 (1916)], 21.7 g. of Cu(NO -3HO, 2.6 g. of telluric acid and 50 ml. of water. The mixture is added to328 g. of a 46 mesh silicon carbide aggregate. The addition is carriedon in such a manner that the evaporation of the water and nitrogen oxideevolution are very rapid. The resulting dry particles of catalyst arefired in an oven for two hours at 1000" F. The weight of the final firedcatalyst containing 5.5 percent of metal oxide composition is 347 g.Empirical formula: Cu Te Pv O A ZOO-ml. portion of the catalyst ischarged into a 400-ml. oxidation reactor. The heated catalyst bed iscontacted With a mixed vapor feed stream having the followingcomposition by volume: isobutylene14.4%, air -73.2%, and steam12.4%. Thereaction is conducted at approximately atmospheric pressure at anaverage temperature of 538 C. The apparent contact time is 2.1 seconds.The reaction products are analyzed by the Orsat and GLC methods. A 42percent conversion of the fed isobutylene is obtained with amethacrolein yield of 46 percent.

Water solubility of reactants was obtained by the use of aphosphovanadate in the above procedure. However, solubility of reactantsmay be achieved conveniently by other means as shown in the procedurebelow.

Example 11 A copper-vanadium-tellurium catalyst of this invention isprepared by following essentially the catalyst preparation procedure ofExample I. The following aqueous mixture is employed in the preparation:A slurried mixture of 14 g. of ammonium vanadate, 21.7 g. of

2.6 g. of telluric acid and 60 ml. of water are added to 328 g. of 4-6mesh silicon carbide aggregate. The catalyst aggregates are fired byheating at 1000 F. for two hours. The weight of the fired catalysthaving 5.1 percent complex is 346 g. Empirical formula: Cu Te V O AZOO-ml. portion of the catalyst is charged into the conventionaloxidation reactor employed in Example I. The heated catalyst bed iscontacted with a mixed vapor feed stream having the followingcompositions by volume: isobutylenel4.4%, air-73%, and steam-12.6%. Thereaction is conducted at approximately atmospheric pressure at anaverage temperature of 478 C. The average contact time is 2.3 seconds.The reaction products are analyzed by the Orsat and GLC methods. A 25percent conversion of the fed isobutylene is obtained with amethacrolein yield of 52 percent.

One problem associated with isobutylene oxidation is the formation oftar-like, non-volatile by-products which may deposit in the catalystbed, on the walls of reactors and pipes or appear in the aqueous mixtureobtained upon quenching the hot gases as they leave the reactor. Bothisobutylene and oxygen are consumed by thi side reaction. It has beendisclosed in US. Ser. No. 247,267, US. Ser. No. 247,268 and US. Ser. No.247,307 that up to about 95 percent of the copper in the catalyst may bereplaced by chromium, cobalt or nickel to yield catalysts which may beused with substantial reduction of tar formation. These catalysts, beingmore complex, are somewhat more expensive to manufacture but the extraexpense is justified if the cost of isobutylene feed should increase, orif isobutylene should happen to become a scarce commodity. Preferredcatalyst compositions are made by reacting the metallic oxides inapproximately the following proportions.

Following is exemplified the preparation and use of a catalyst in whicha portion of the copper is replaced by chromium.

A copper chromium-tellurium-phosphorus-vanadiumoxygen catalyst complexis prepared by using the following aqueous mixture: 7.9 g. of ammoniumphosphovanadate [prepared by the process described by A. Rosenheim andM. Pieck, Z. Anorg. Allgem. Chem. 98, 223 (1916)], 7.3 g. of Cu(NO -3HO, 1.15 g. of telluric acid, 6.0 g. of Cr(NO -9H O, and 50 ml. of Water.Empirical formula: Cu Cr TePV O There is exemplified below thepreparation and use of a catalyst in which a portion of the copper isreplaced by cobalt.

A cobalt-copper-tellurium-phosphorus-vanadium-oxygen catalyst complex isprepared by using the following aqueous mixture: 7.9 g. of ammoniumphosphovanadate [prepared by the process described by A. Rosenheim andM. Pieck, Z. Anorg. Allgem. Chem. 98, 223 (1916)] 4.8 g. of Cu(NO -3H O,11.6 g. of Co(NO -6H O, 1.15 g. telluric acid and 50 ml. of water.Empirical formula: COBCU4TPV12O4G 5.

The modification of. the catalyst by substituting nickel for a part ofthe copper is illustrated below.

A nickel-copper-tellurium-phosphorus-vanadium-oxygen catalyst complex isprepared by using the following aqueous mixture: 7.9 g. of ammoniumphosphovanadate [prepared by the process described by A. Rosenheim andM. Pieck, Z. Anorg. Allgem. Chem. 98, 223 (1961)]. 7.3 g. of Cu(NO -3HO, 3.4 g. of Ni(NO -6H O, 1.15 g. of telluric acid and 50 ml. of water.Empirical formula: Nl CU5TPV12O43 5.

(3) Catalyst regeneration.The procedure for catalyst regeneration isremarkable for its simplicity.

A cc. (158 g.) portion of a catalyst which has been used more than 2000hours and which shows low activity and selectivity is screened to removeapproximately 10 percent of the active catalyst component present asloose, nonadherent powder. The spent catalyst is then treated with asolution of catalyst reagents in the same manner as fresh uncoatedcatalyst support and fired.

(4) Construction of catalyst bed.The catalyst bed is preferablystationary and so positioned that reactants flow downward verticallythrough the bed. Free space in the reactant entry zone is to be avoided,because of the possible occurrence of non-catalytic gas phase oxidation.Voids in the reactor are preferably packed with particles of inertrefractory material so as to discourage free space reactions.

(B) REACTION CONDITIONS (1) Reactant rati0s.-The hydrocarbon feed streammay contain from about 8 percent isobutylene to substantially pureisobutylene in operation of the process.

The complete reactor feed consists preferably of preheated hydrocarbon,steam or other inert diluent, and air, which are introduced into thereactor with prior mixing. It is recommended that approximately thefollowing molar ratios of reactants be maintained in the feed streams:

1 mole isobutylene/ 1.5 moles O 1 to 15 moles H O or other diluent(preferably about 1.5 moles) The presence of steam or other inertdiluent prevents erratic behavior of the system. The concentrations ofboth isobutylene and oxygen in the gaseous stream through the reactordiminish as the reaction proceeds, resulting in a decrease in reactionrate. It may be desirable to take steps to compensate for this effect soas to obtain the best possible conversion. Otherwise, unreactedisobutylene may be recovered and recycled.

(2) Temperature-Although the operable temperature range is very broad,for economical operation it is recommended that the temperature be keptwithin the range of about 350 to 525 C. Preferably, the temperature isonly permitted to vary between about 430 and 480 C., with the controlpoint set at about 440 C. With adequate provision for heat exchange,continuous cooling will be employed during operation and fluctuation oftemperature will be infrequent. Erratic and violent temperaturefluctuations are not characteristic of the process and may be taken asan indication of failure to maintain constant feed ratios, or perhapsthe presence of excessive oxygen concentration in the system.

(3) Pressure.Preferred pressure is one atmosphere plus sufficientadditional pressure to overcome the resistance of the porous catalystbed to gas flow. The catalyst bed should offer as little resistance togas flow as is practically feasible, so as to create the minimumpressure differential in the system.

(4) Throughput rate.Throughput rate may vary greatly, one volume of feedgas per volume of catalyst bed every 1 to 15 seconds being reasonable. Apreferred range is one volume of feed gas per volume of catalyst bedevery 2.5 to 3 seconds. At high linear velocities of gas flow throughthe catalyst bed, better rates of production of methacrolein per hourper volume of catalyst bed can be obtained but the contact time is shortand control of this condition becomes more critical. Since the obtainingof the higher production rate is accompanied by this need for moreaccurate control, some may chose to operate at lower throughput rates,where there are fewer control problems.

(C) RECOVERY OF PRODUCT The product may be recovered by conventionalmeans, that is, a water quench of the hot gases, followed by scrubbing,distillation and other steps, including recovery of unreactedisobutylene and other hydrocarbons. Unreacted propylene, if present,should be removed and not recycled, since propylene is oxidized only toa negligible extent in the process and will accumulate in the recyclestream if not eliminated.

The oxidation of isobutylene without substantial effect on propylene, ifpresent, is clear evidence of the specific nature of the combination ofcatalyst and reaction conditions in the process as disclosed.

What is claimed is:

1. A process for converting isobutylene to methacrolein comprisingreacting isobutylene at a temperature within the range of 350 to 525 C.in the presence of oxygen and an oxide composition, the empiricalformula of which lies within the limits e+1 1.5+0.2 1.1+0.1 12 approx.45

said oxide composition being produced by heating an intimate mixture ofthe oxides to a temperature at least as high as that employed inconverting isobutylene to methacrolein and being on the surface of arefractory solid which is essentially non-reactive to the metal oxidecomposition and possesses a surface area of less than about 10 squaremeters per gram.

References Cited Throne et al.: Inorganic Chem, 2nd edit, page 561,1949, Interscience Publishers.

LEON ZITV'ER, Primary Examiner R. H. LILES, Assistant Examiner US. Cl.X.R. 252-437, 439

ffiyggg" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3 r 499 Dated March 10 I 1970 Inventor(s) Donald M. Coyne and RogerP. Cahoy It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 6, Claim 1, line 14, that portion of the formula reading:

9+1 1.s+o.2 1.1+o.1 shuld read 9 1 1.5 o.2 1.1 0.1

SIGA'F F W S FMED AUG 251970 (SEAL) 1168i: A WILLIAM E. mm, an. Edward MFl 'o I fiomiagtqaez: of Patents Attesting Off c

1. A PROCESS FOR CONVERTING ISOBUTYLENE TO METHACROLEIN COMPRISINGREACTING ISOBUTYLENE AT A TEMPERATURE WITHIN THE RANGE OF 350 TO 525*C.IN THE PRESENCE OF OXYGEN AND AN OXIDE COMPOSITION, THE EMPIRICALFORMULA OF WHICH LIES WITHIN THE LIMITSCU(9+1)TE(1.5+0.2)P(1.1+0.1)V(12)O(APPROX. 45) SAID OXIDE COMPOSITIONBEING PROCUDED BY HEATING AN INTIMATE MIXTURE OF THE OXIDES TO ATEMPERATURE AT LEAST AS HIGH AS THAT EMPLOYED IN CONVERTING ISOBUTYLENETO METHACROLEIN AND BEING ON THE SURFACE OF A REFRACTORY SOLID WHICH ISESSENTIALLY NON-REACTIVE TO THE METAL OXIDE COMPOSITION AND POSSESSES ASURFACE AREA OF LESS THAN ABOUT 10 SQUARE METERS PER GRAM.